LICENSE.md: add vf_eq

Found-by: jamrial
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

LICENSE.md

@@ -30,6 +30,7 @@ Specifically, the GPL parts of FFmpeg are:
     - vf_colormatrix.c
     - vf_cropdetect.c
     - vf_delogo.c
+    - vf_eq.c
     - vf_fspp.c
     - vf_geq.c
     - vf_histeq.c